I just checked. The only presence of this feature in the Bash man page is under REDIRECTION with the following, as the fifth and sixth elements of the list:

     /dev/tcp/host/port
       If host is a valid hostname or Internet address, and port is an integer
       port number or service name, bash attempts to open the corresponding
       TCP socket.
     /dev/udp/host/port
       If host is a valid hostname or Internet address, and port is an integer
       port number or service name, bash attempts to open the corresponding
       UDP socket.

It's not a feature with a large documentation footprint. I've known about it for a while, but mostly only in the context of security too. I have wondered whether the majority use of this feature is to provide hacked network shells before. It's probably a feature that never should have been added, though I understand the initial appeal.

It's a terrible "feature". Not only is it poorly documented (as noted) and redundant to common shell utilities (like nc), it's also implemented in a way that confusingly implies that it's part of the operating system. (And if your OS ever implemented a "real" /dev/tcp, I suspect that this Bash feature would make it inaccessible.)

We've used it for simple health ping scripts before in systems where bash is the only language guaranteed to be available and compiling a binary was overkill.

I've also used it to issue Redis and other text based protocol commands without having to have a large runtime or library.

But in both those scenarios the environment was pretty restrictive.

"important capabilities"? It's a fairly exotic feature nearly nobody is actually using, so the only people I'd expect to know about it are old-timey sysadmins and security people who've looked into stuff like discussed in the article. And while "lead of the anti-abuse team" is a security role, there are many possible backgrounds where you'd never come across this, and anti-abuse likely is working on a higher level.

Testing for stuff like that would be worse trivia checks than the algorithm-bingo people like to complain about in Google developer interviews.

Maybe the jobs are so highly sought after because they understand that practical knowledge is different from esoteric knowledge, and it's worth having gaps in knowledge of bash arcana if it means that you spent your time learning more important things.

The feature is pretty useless because it doesn't easily get you a two-way pipe, and there are lots of easier-to-use, more reliable ways to get a two-way pipe (or a one-way pipe, even).

Just to clarify to the commenters: The reason it is "important" IMO is because it is a liability not an asset. I do not even use Bash myself; still, I am aware that it has this liability^W capability.